1. Field of the Invention
The present invention relates to a process for manufacturing deep through vias in a semiconductor device and to a semiconductor device made thereby.
2. Discussion of the Related Art
As is known, several electronic or micro-electromechanical semiconductor devices are formed by a number of semiconductor chips assembled together. For example, many MEMS (micro-electromechanical systems) sensors comprise a first chip, wherein a micro-electromechanical structure is formed, and a second chip, bonded and electrically connected to the first chip, where the necessary control circuitry is housed. Other devices can comprise even more than two chips.
Obviously, to electrically connect the different chips it is necessary to provide appropriate conductive connection structures. In less recent devices, said structures included wire connections, which, however, have the disadvantage of being relatively brittle and increase the overall dimensions of the device.
In order to overcome these drawbacks, the use of through conductive vias that traverse the substrate of one of the chips and enable setting-up of a connection between the opposite faces of the chip itself has been proposed. Examples of through vias are described in EP-A-1 151 962, which is incorporated herein by reference. Basically, portions of the substrate of a wafer or of a chip are insulated laterally and form a conductive path through the chip, without increasing the encumbrance.
Also the fabrication of known through vias, however, is not free from drawbacks. In particular, the known processes envisage thinning of the substrate in which the through vias are made. More precisely, cylindrical or prismatic pillars of the substrate are delimited by forming trenches on a front face of the substrate itself down to a predetermined depth. After the trenches have been filled with dielectric material, the substrate is thinned by grinding a rear face, until the pillars and the trenches filled with dielectric material come to the surface. At this point, the pillars are completely insulated from the remainder of the substrate and form through vias.
The operation of grinding, however, subjects the substrate to a remarkable mechanical stress and can cause microcracks in the crystalline structure. In some cases, the damage is particularly serious and causes the substrate to be rejected. In general, the average quality of the substrate machined in the way described is impaired.